Provides information to AWS about your VPN customer gateway device.
The customer gateway is the appliance at your end of the VPN
connection. (The device on the AWS side of the VPN connection is the
virtual private gateway.) You must provide the Internet-routable IP
address of the customer gateway's external interface. The IP address
must be static and may be behind a device performing network address
translation (NAT).

For devices that use Border Gateway Protocol (BGP), you can also
provide the device's BGP Autonomous System Number (ASN). You can use
an existing ASN assigned to your network. If you don't have an ASN
already, you can use a private ASN (in the 64512 - 65534 range).

NOTE: Amazon EC2 supports all 2-byte ASN numbers in the range
of 1 - 65534, with the exception of 7224, which is reserved in the
us-east-1 region, and 9059, which is reserved in the eu-west-1 region.

IMPORTANT: You cannot create more than one customer gateway
with the same VPN type, IP address, and BGP ASN parameter values. If
you run an identical request more than one time, the first request
creates the customer gateway, and subsequent requests return
information about the existing customer gateway. The subsequent
requests do not create new customer gateway resources.